Gemstones
A gemstone or gem (also called a precious or semi-precious stone, a fine gem, or jewel) is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments.However certain rocks (such as lapis lazuli), or organic materials that are not minerals (such as amber or jet), are also used for jewelry, and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone. Apart from jewelry, from earliest antiquity until the 19th century engraved gems and hardstone carvings such as cups were major luxury art forms; the carvings of Carl Fabergé were the last significant works in this tradition.
Characteristics and classification
The traditional classification in the West, which goes back to the Ancient Greeks, begins with a distinction between precious and semi-precious stones; similar distinctions are made in other cultures. In modern usage the precious stones are diamond, ruby, sapphire and emerald, with all other gemstones being semi-precious.This distinction reflects the rarity of the respective stones in ancient times, as well as their quality: all are translucent with fine color in their purest forms, except for the colorless diamond, and very hard, with hardnesses of 8 to 10 on the Mohs scale. Other stones are classified by their color, translucency and hardness. The traditional distinction does not necessarily reflect modern values, for example, while garnets are relatively inexpensive, a green garnet called Tsavorite, can be far more valuable than a mid-quality emerald. Another unscientific term for semi-precious gemstones used in art history and archaeology is hardstone. Use of the terms 'precious' and 'semi-precious' in a commercial context is, arguably, misleading in that it deceptively implies certain stones are intrinsically more valuable than others, which is not the case.
In modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. The first characteristic a gemologist uses to identify a gemstone is its chemical composition. For example, diamonds are made of carbon (C) and rubies of aluminium oxide (Al2O3). Next, many gems are crystals which are classified by their crystal system such as
cubic or trigonal or monoclinic. Another term used is habit, the form the gem is usually found in. For example diamonds, which have a cubic crystal system, are often found as octahedrons.
Gemstones are classified into different groups, species, and varieties. For example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Other examples are the Emerald (green), aquamarine (blue), red beryl (red), goshenite (colorless), heliodor (yellow), and morganite (pink), which are all varieties of the mineral species beryl.
Gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and luster. They may exhibit pleochroism or double refraction. They may have luminescence and a distinctive absorption spectrum.
Material or flaws within a stone may be present as inclusions.
Gemstones may also be classified in terms of their "water". This is a recognized grading of the gem's luster and/or transparency and/or "brilliance". Very transparent gems are considered "first water", while "second" or "third water" gems are those of a lesser transparency.
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| Gemstones |
Diamond
Diamond, the most famed and fabled of all gemstones, is very unique in many ways. Renowned for being the hardest substance on earth, its sparkling fire, durability, and rarity make Diamond the most prized of all gems. No gemstone contains as much allure and interest as does Diamond.Most Diamonds used as gemstones are colorless or very faintly colored. However, colored Diamonds, known as "Fancies", can be extremely rare and valuable, and the most valuable gemstones ever known have been Fancy Diamonds. In fact, Fancy Diamonds are the most valuable substances known to man, with vivid colored Diamonds historically being sold for more than a million dollars per carat.
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| Fancy Blue Diamond |
Amethyst
Amethyst is one of the most popular gemstones, and has been considered valuable since ancient times. Its name derives from the Greek "amethystos", which means "not drunken", as Amethyst in antiquity was thought to ward off drunkenness. Amethyst was once highly regarded among the precious gemstones like Ruby and Emerald, but discoveries of huge Amethyst deposits since the 1800's have made Amethyst fairly inexpensive and very obtainable. Amethyst colors range from light to dark purple, and the transparent deep purple colors are the most highly regarded.
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Amethyst is the purple variety of the mineral Quartz, and is its most famous and valuable gem variety. Quartz also contains other gemstones such as Citrine, Rose Quartz, and Smoky Quartz. The color of Amethyst is most often caused by iron impurities, though it can also be colored by natural radiation exposure. Amethyst is sometimes heat treated to deepen the color, or to transform it into Citrine. Some forms of Amethyst may also change to a light green color upon heat treatment, and such stones are given the name Prasiolite, or "Green Amethyst", as it is more commonly known in the gem trade.
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| Deep Purple Amethyst Cluster |
Sapphire
Sapphire is the most precious and valuable blue gemstone. It is a very desirable gemstone due to its excellent color, hardness, durability, and luster. In the gem trade, Sapphire without any color prefix refers to the blue variety of the mineral Corundum. However, the term Sapphire encompasses all other gem varieties and colors of Corundum as well, excluding Ruby, the red variety of Corundum, which has its own name since antiquity.
The most valuable color of Sapphire is a cornflower blue color, known as Kashmir Sapphire or Cornflower Blue Sapphire. Another extremely valuable Sapphire form is the very rare, orange-pink Padparadschah. An exotic type of sapphire, known as Color Changing Sapphire, displays a different color depending on its lighting. In natural light, Color Changing Sapphire is blue, but in artificial light, it is violet. (This effect is the same phenomenon well-known in the gemstone Alexandrite). Yellow and pink Sapphire have recently become very popular, and are now often seen in jewelry.
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| Blue Sapphire |
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| Pink Sapphire |
Alexandrite
Alexandrite is the highly regarded color changing variety of Chrysoberyl. The color of Alexandrite changes under different lighting conditions. If viewed in daylight, its color is greenish blue to dark yellow-green. If viewed in incandescent or candle light, its color is pink to red. Alexandrite is a very rare and highly valuable gemstone, and until recently was extremely difficult to obtain due to its rarity. However, new sources in Brazil and Tanzania have made this gemstone available and more mainstream on the gemstone market.
Alexandrite was first discovered in Russia in the early 1800's. It was named in honor of Alexandar Nicholavich, who was later to become the Russian Czar Alexander II. Legend has it that the gemstone was discovered on the future Czar's birthday and named in his honor, though the factual nature of this is disputed.
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| Alexandrite |
Garnet
Garnet is not a single mineral, but describes a group of several closely related minerals. Garnets come in a variety of colors and have many different varieties. However, the most widely-known color of Garnet gemstones is dark red. When the term "Garnet" is used, it is usually connotative of the dark red form; other color Garnets are usually given more descriptive gemstone terms.
Almandine and Pyrope are the most widely used Garnet gemstones. Though Almandine is the most common Garnet, it is usually opaque and not fit for gemstone use. Only the less common transparent dark red forms of Almandine are used as gemstones. Pyrope is especially noted for its transparency and frequent lack of flaws or inclusions. A rose-red to violet variety of Pyrope (or intermediary between Almandine and Pyrope) is known as Rhodolite, and is a very well represented in the gem trade.
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| Pyrope Garnet |
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| Rhodolite garnet |
Opal
Opal is the most colorful of gems. Its splendid play of color is unsurpassed, and fine examples can even be more valuable than Diamond. The play of color consists of iridescent color flashes that change with the angle at which the stone is viewed. This phenomenon is often called opalescence. The play of color may consist of large, individual flashes of color (known as schillers), or may be of tiny, dense flashes. The intensity and distribution of the color flashes is a determining factor in the value of an Opal.
Opals displaying play of color are known as Precious Opals, and opals lacking play of color are known as Common Opals. Gems can be cut from both the precious and common forms, but Precious Opal is the primary gem form of this stone. There are many varieties of both precious and common Opals. The most desired and beautiful form of opal is Black Opal, which is opal with a dark blue, dark green, or black background with a strong play of color. Next in importance is White Opal, which is Opal with a light colored body color (white, yellow, cream, etc.) with strong play of color. Also important is Fire Opal, or Mexican Fire Opal, which is a transparent to translucent deep-orange red form of Common Opal. Fire Opal can also display play of color, and this is a rarity called Precious Fire Opal.
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| Black Opal |
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| White Opal |
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| Fire Opal |
Emerald
Emerald, the green variety of Beryl, is the most famous and valuable green gemstone. Its beautiful green color, combined with durability and rarity, make it one of the most expensive gemstones. Deep green is the most desired color in Emeralds. In general the paler the color of an Emerald, the lesser its value. Very pale colored stones are not called Emeralds but rather "Green Beryl". They are sometimes heat treated, which causes their color to turn blue and transform into Aquamarine.
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| Emerald |
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| Single Colombian Emerald Crystal |
Ruby
Ruby is distinguished for its bright red color, being the most famed and fabled red gemstone. Beside for its bright color, it is a most desirable gem due to its hardness, durability, luster, and rarity. Transparent rubies of large sizes are even rarer than Diamonds. Ruby is the red variety of the mineral Corundum. Sapphire, the other gem variety of Corundum, encompasses all colors of Corundum aside from red. In essence, Ruby is a red Sapphire, since Ruby and Sapphire are identical in all properties except for color. However, because of the special allure and historical significance, Ruby has always been classified as an individual gemstone, and is never identified as a form of Sapphire (though some purplish-red colors may straddle the line of being classified as either Ruby or Sapphire).
The color of Ruby ranges from bright red to dark reddish-brown. The most preferred color is a deep blood red with a slightly bluish hue. Such Ruby is known as "Burmese Ruby" or "Pigeon's Blood Ruby". Ruby from Burma is famous for its exceptional coloring, and has traditionally produced the finest Rubies. However, Burmese Ruby rarely exceeds several carats; large flawless Burmese Rubies can be worth millions of dollars. Many Rubies on the market are from Thailand, and these Rubies have a less-desirable brownish hue, though they often can be heat treated to improve color. Heat-treating a Ruby can also increase its transparency by removing tiny internal flaws.
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| Ruby |
The color of Ruby ranges from bright red to dark reddish-brown. The most preferred color is a deep blood red with a slightly bluish hue. Such Ruby is known as "Burmese Ruby" or "Pigeon's Blood Ruby". Ruby from Burma is famous for its exceptional coloring, and has traditionally produced the finest Rubies. However, Burmese Ruby rarely exceeds several carats; large flawless Burmese Rubies can be worth millions of dollars. Many Rubies on the market are from Thailand, and these Rubies have a less-desirable brownish hue, though they often can be heat treated to improve color. Heat-treating a Ruby can also increase its transparency by removing tiny internal flaws.
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| Blood Red Ruby Crystal |
Peridot
Peridot is a well-known and ancient gemstone, with jewelry pieces dating all the way back to the Pharaohs in Egypt. The gem variety of the mineral Olivine, it makes a lovely light green to olive-green gemstone. The intensity of color depends on the amount of iron present in a Peridot's chemical structure; the more iron it contains the deeper green it will be. The most desirable color of Peridot is deep olive-green with a slight yellowish tint. Deeper olive-green tones tend to be more valuable than lighter colored greens and yellowish-greens.
The history of Peridot is intrinsically tied to the tiny Egyptian island of St. John (Zabargad) in the Red Sea, which was the one of the only ancient sources of gem Peridot. This deposit has been totally exhausted, though fairly significant deposits have since been discovered, especially since the 1990's.
Topaz
Topaz makes an ideal gem. A good hardness and desirable colors, combined with a relative abundance and availability makes it one the most popular gemstones. The most valuable colors of Topaz are the golden orange-yellow type, called Imperial Topaz, and the dark pinkish-red and orange-red colors. Value increases with a deepness of color in orange and reddish hues. The most commonly used colors of Topaz in jewelry are the blue types. It was not until this past century that blue Topaz became widespread on the gem market, since virtually all blue gem Topaz is irradiated and heat treated.
Turquoise
Turquoise is an ancient gemstone, and has been highly regarded in many of the world's civilizations. Among the ancient empires it is best known among the Persian and Native American civilizations, where it was the most popular ornamental gemstone. Turquoise today remains a popular gemstone, and is one of the most important opaque gemstones. It is highly regarded due to its unique turquoise-blue color, and is the only gemstone to have an exclusive color named after it.
The word Turquoise dates back to the 17th century, when trading routes brought Turquoise from Persia through the Middle East towards Europe. The traders passed through Turkey, known as "Turquie" in French, and the locals named the material "Turquies" ("Turkish") in reference to its coming from Turkey.
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The history of Peridot is intrinsically tied to the tiny Egyptian island of St. John (Zabargad) in the Red Sea, which was the one of the only ancient sources of gem Peridot. This deposit has been totally exhausted, though fairly significant deposits have since been discovered, especially since the 1990's.
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| Peridot |
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| Pridot crystal |
Topaz makes an ideal gem. A good hardness and desirable colors, combined with a relative abundance and availability makes it one the most popular gemstones. The most valuable colors of Topaz are the golden orange-yellow type, called Imperial Topaz, and the dark pinkish-red and orange-red colors. Value increases with a deepness of color in orange and reddish hues. The most commonly used colors of Topaz in jewelry are the blue types. It was not until this past century that blue Topaz became widespread on the gem market, since virtually all blue gem Topaz is irradiated and heat treated.
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| Blue Topaz |
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| Pink Topaz |
Turquoise
Turquoise is an ancient gemstone, and has been highly regarded in many of the world's civilizations. Among the ancient empires it is best known among the Persian and Native American civilizations, where it was the most popular ornamental gemstone. Turquoise today remains a popular gemstone, and is one of the most important opaque gemstones. It is highly regarded due to its unique turquoise-blue color, and is the only gemstone to have an exclusive color named after it.
The word Turquoise dates back to the 17th century, when trading routes brought Turquoise from Persia through the Middle East towards Europe. The traders passed through Turkey, known as "Turquie" in French, and the locals named the material "Turquies" ("Turkish") in reference to its coming from Turkey.
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| Turquoise |
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| Bright Kingman Turquoise Nugget |
World Gemstones Map
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